High-frequency tube structure



Aug. 26, 1952 E. L. GINZTON 2,603,670

HIGH-FREQUENCY TUBE STRUCTURE Original Filed Jan. 29, 1942 INVENTOR.[OW/9RD L $m/z7'0/s/ A TTOR/VEY Patented Aug. 26, 1952 2,608,678HIGH-FREQUENCY TUBE STRUCTURE.

Edward L. Ginzton, Redwood, Calif., assignor to The Sperry Corporatlomacorporation of Delaware Original application January 29, 1942, SerialNo. 428,682. Divided and this application December 14, 1946, Serial No.716,211

10 Claims. 1

The present invention relates to the art including electron dischargedevices and is more particularly directed to improvements in suchdevices utilizing cavity resonators and adapted to operate at ultra-highand super-high frequencies (also termed microwaves) "of the order ofabout 300 megacycles per second and higher.

The present application is a division of application Serial No. 428,682for High Frequency Tube Structure filed January 29, 1942 issued asPatent No. 2,414,785 on January21, 1947.

As disclosed in United States Patents No. 2,280,824 and No. 2,391,016,it is known to provide a vacuum envelope containing the electrodesproducing and interacting with an electron stream, and to provide acavity resonator external of the envelope and coupled through theenvelope to the stream-interacting electrodes. An example of such astructure is shown in Fig. 7 of the above-mentioned Patent No. 2,391,016wherein this type of apparatusis included in a reflex klystron tube. l I

Especially where capacitive coupling between the external resonator andthe internal electrodes is used, difliculty may be encountered becauseof the leakage of high frequency energy through the dielectric materialof the envelope between the resonator and the'electro'des within theenvelope. This effect decreases the useful Y.

power output and also impairs the effectiveness of the resonator bylowering its shunt impedance.

The present invention is directed toward improved apparatus forovercoming these difficulties. I

According to the present invention, a microwave filter structure isprovided in conjunction with external cavity resonators of this type soas to present substantially a short circuit or zero impedance betweenthe internal electrodes and the external resonator. From anotherviewpoint, this structure provides a wave trap arrangement preventingmicrowave leakage.

Accordingly, it is an object of the present invention to provideimproved electron'discharge apparatus having cavity resonator structuresexternal to the vacuum envelope and substantially minimizing undesiredleakage from such reso nator.

In particular, it is an object of th e present invention to provide animproved reflex klystron device wherein the beam-producing andcontrolling electrodes are contained within a vacuum envelope with acavity resonator external to the envelope and capacitively coupled totheinternal electrodes, means being provided according to the inventionforminimizing leakage from betweenthe resonator'and its electrodesandfor providing a substantially zero impedance therebetween. v

Other'objects and advantages will become ap parent from the followingspecification taken in connection with the appended drawings, in whichFig. 1 is a longitudinal cross-sectional view of a preferred embodimentof the present invention, and

Fig. 2 is a cross-sectional view of the device of Fig. 1 taken alongline 22 thereof, and turned 90 degrees.

Referring to the drawing, there is shown an evacuated envelope having atubular smalldiameter section 89, and an enlarged section [ll connectedthereto by a connecting portion I. Preferably, envelope section 89 isformed of dielectric material having low-loss at the operating frequencyand may, for example, be formed of quartz. Section [0 may be formed of aconventional soft glass suitable for forming into a press such as shownat 93, the connecting section I being a graded seal for connecting thesetwo different materials. Contained within envelope section 89 is acathode 90 supported upon an insulator 80, which in turn, is supportedfrom press 93 by rigid leads 92. Adjacent the upper end of cathode 98,which is its emitting surface, are a pair of grids B5, 88 formed, forexample, of radially inward-directed strips fixed to a supportingencircling ring. Grids 85, 88 are supported at the adjoining ends ofrespective tubular members 84, 81, which, are positioned within envelopesection 89 and close to the inner surface thereof. On the side of grid85 opposite cathode 90 is a reflector electrode 9| rigidly supported bya lead 10 from the upper end of envelope section 89. Tubular members 84,81 have respective leads 30, 3|, which serve to position these membersand to provide leads for applying suitable potentials thereto. I

Surrounding the envelope section 89 is a cavity resonator structure 82,having a pair of tubular portions 83, 8 6 closely surrounding envelope89 and capacitively coupled to the tubular members 84, 81 respectivelythrough the vacuum envelope 89. Resonator 82 also has an outercylindrical wall 96 connected to the tubular members 83, 86 byrespective disc walls H, 12. In this way, the field within resonator 82,and especially that portion thereof between the juxtaposed ends oftubular members 83, 86, is impressed between electrodes 85, 88 by meansof the capacitive coupling between tubular members 83 and 84 and between86 and 81.

This structure thus far described is very similar to that shown in Fig.'7 of the above mentioned Patent No. 2,391,016. However, serious lossofenergy which may result by leakage out through the vacuum envelope 89from between the capacitive elements 83, 84 and 86,

8'! is greatly minimized in the present construction. The outercylindrical wall'of resonator is 82 is extended in both directions toform the outer wall of cavities 9'5, 98 on each side thereof. The endsof cavity 81, 98 are closed by apertured discs 99, I60 respectivelythereby forming an enclosing vessel having three cavities 82, 91 and 98therein. Tubular conductors llll, l02'snugly fitting the vacuum envelope89 are fastened within the apertures of discs 99, I respectively;whereby a portion of each of these tubes I0 I, I02 extends into thecavities 91, 98 and a portion extends beyond the discs 99, 1'80respectively. Tubes HM, 83, 8 and 102 are each made substantiallyelectrically a quarter-wavelength long, the distance between tubes Niland 83 and that between tubes 86 and 192 also being substantiallyelectrically equal to a quarter-wavelength of the operating frequency.

The manner in which this construction minimizes microwave energyleakage, will be apparent from the following theoretical considerations.Tube 32 and member 81 form a coaxial transmission line of length equalto one-quarter-wavelength and of a characteristic impedance which may bedesignated by Z1. The impedance at point 3 viewed outwardly from theresonator is largely resistive and may be designated by R. By virtue ofthe transmission line 102, 81, this resistance R, istransformed to animpedance equal to viewed outwardly from point ,4. If the characteristicimpedance defined by cavity 98 be designated as Z2, the impedance atpoint 5 viewed toward point 4 is V Z2 R X (a) Tubes 36 and 81 form aquarter-wavelength section of concentric transmission line of characteristic impedance equal to Z1. Therefore, the impedance at point 6v viewedoutwardly is given by the following expression:

Since Z1 is relatively small and Z2 is relatively large, this last valueof impedance is very small so that little or no energy can leak down theenvelope 89 to the external point 3. It will be understood that similarconsiderations apply with respect to leakage upwardly from the gapbetween grids 8'5 and 88.

For withdrawing useful output from resonator 82, a concentrictransmission line terminal H, having a coupling loop l2 perpendiculartothe plane of the section of Fig. 2 is insulatedly supported fromresonator 82 by meansof an insulating-bushing is so that resonator '82may be held at any desired potential relative to line i E. Tuning ofresonator 82 may be accomplished by means of a plug M threaded to thewall of resonator 82. Adjustment of the extension of screw 4 l4 intoresonator 82 accomplishes tuning of the resonator in the mannerdisclosed in United States Patent 2,259,690. Similar or other tuningmeans may be provided in cavities 9'! and 98 as desired.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departure from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanyingdrawingsshall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. In a. high frequency tube structure, means for producing an electronstream, an evacuated substantially cylindrical insulating envelopesurrounding said stream, spaced grid members within said envelope, ahollow resonator capacitively coupled through said envelope to said gridmembers for setting up an alternating electric field therebetween forcoacting with said electron stream, and means including a portion ofsaid envelope and said resonator providing an impedance between saidgrid members and the respective ends of said envelope for reducing, theescape of electromagnetic energy endwise of said envelope, saidlast-named means including a quarter wavelength coaxial 7 transmissionline having open ends. a

2. Apparatus as defined in claim 1 wherein said last-named meansincludes resonant chamber means for loading the end 'of saidtransmission linemost remote from said grid members with a relativelyhigh impedance.

3. A high frequency tube structure as defined in claim 2 wherein saidcoaxial transmission line is coaxial with said cylindrical envelope, oneend of said line extending substantially to one of said grid members,and said resonant chamber means communicating with said alternatingelectric field via the material of said envelope. 1

4. A high frequency tube structure as defined in claim 1 wherein one endof said coaxial transmission line extends to the juncture of said gridmembers and said hollow resonatonsaid linebeing coaxial with the path ofsaid-electron stream, and a further open-ended quarter wavelengthtransmission line is provided, said further line be.- ing spaced 2,quarter wavelength from the end of said first-mentioned line most remotefrom said grid members, both said lines having inner and outerconductors in contact with said envelope.

5. In a high frequency tube structure, electronstream-producing means,an evacuated insulating envelope surrounding the path of said stream, atubular sleeve coaxial with said path, spaced gridmembers within saidenvelope and defining a gap, one of said grid members being locatedadjacent one end of said sleeve, a hollow resonator capacity-coupledthrough said envelope to said grid members for setting up an alternatingelectric field there'oetween for coacting with said electron stream, aportion of said sleeve and a portion of said resonator providing anopen-ended quarter wavelength coaxial transmission line having one. endadjacent said gap, and resonant chamber means for providing a variableimped-.

ance along the length of said envelope substantially a distanceelectrically equal to a quarter wavelengthextending from the other endof said transmission line in a direction away from said gap, whereby theescape of electromagnetic energy endwise of said envelope is minimized.

6. A high frequency tube. structure comprising an evacuated insulatingenvelope, tube electrodes within said envelope disposed so that theiropposed ends are somewhat spaced apart, a hollow resonator surroundingsaid envelope, said resonator being coupled to said tube electrodes andserving to establish an alternating electric field between the opposedend portions of said tube electrodes, means for setting up an electronstream within said envelope coacting upon said alternating electricfield, and filter means comprising cavity members located at oppositeends of said hollow resonator and surrounding said envelope, said cavitymembers being capacity coupled to said tube electrodes and providingimpedance means variable along the length 01' said envelopesubstantially a distance electrically equal to a quarter wavelength forblocking the escape of energy endwise of said insulating envelope, saidresonator cooperating with said envelope to provide a quarter wavelengthtrap for further blocking the escape energy endwise of said envelope.

'7. A high frequency tube structure comprising an evacuatedsubstantially cylindrical envelope, means within said envelope forproducing an electron stream, a pair of spaced electrodes within saidenvelope along the path of said stream and defining a gap therebetween,a pair of first tubular members outside said envelope having a gapregistering with said first gap, said first members being electricallyone-quarter-wavelength long at the operating frequency, means coupled tosaid members and defining a cavity resonator therewith, and means forpresenting leakage of high frequency energy from between said electrodesand said members, said last-named means comprising a pair of furtherquarter-wavelength tubular members each surrounding said envelope andspaced a quarter-wavelength from a respective one of said first members,and means coupled between one of said first tubular members and one ofsaid further tubular members and defining therewith a cavity having ahigh characteristic impedance for minimizing energy leakage.

8. Tube structure as in claim 7 further including a pair of tubularmembers within said envelope connected respectively to said electrodesand coaxial with said first and further tubular members, and formingtherewith over their coextensive portions coaxial line sections of lowcharacteristic impedance.

9. A high frequency tube structure comprising an evacuated substantiallycylindrical envelope, means within said envelope for producing anelectron stream, a pair of spaced electrodes within said envelope alongthe path of said stream and defining a gap therebetween, a pair of firsttubular members outside said envelope having a gap registering with saidfirst gap, said members be ing a, quarter-wavelength long at theoperating frequency, a second tubular member within said first envelopeconnected to one of said electrodes and coaxial with said first tubularmembers means coupled to said first members and defining a first cavityresonator therewith, means comprising a, third quarter-wavelengthtubular member surrounding the envelope and spaced a quarter-wavelengthfrom the end of one of said pair of tubular members most remote fromsaid electrodes, and means including a portion of said first cavityresonator defining means and a portion of said third member coupledbetween said one of said first tubular members andsaid third furthertubular member and defining a second cavity resonator having a highcharacteristic impedance, one of said first members and said thirdmember forming with the co-extensive portions of said second membercoaxial line sections of low characteristic impedance, whereby energyleakage is minimized.

10. An electron discharge device comprising a vessel having a portiondefining a cylindrical, metallic concave surface, a unitary electrodeassembly within said vessel including a pair of cooperative electrodes,and means mounting said electrode assembly within said vessel includinga cylindrical metallic member connected electrically to one of saidelectrodes and a cylinder of dielectric material, surrounding saidcylindrical metallic member, said cylinder of dielectric material beinglocated immediately adjacent said cylindrical concave surface anddefining a con denser therewith and with said cylindrical member.

EDWARD L. GINZTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,128,234 Dallenbach Aug. 30,1938 2,163,589 Dallenbach et a1. June 27, 1939 2,167,201 Dallenbach July25, 1939 2,391,016 Ginzton et al Dec. 18, 1945 2,411,299 Sloan Nov. 19,1946

